Dopaminergic metabolism in various rat brain areas after L-dopa loading

The time course of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-methoxytyramine (3-MT) and 3-methoxytyrosine (3-O-Medopa) concentrations in rat brain after treatment with L-dopa + benserazide has been investigated in the striatum, hypothalamus, hippocampus and cerebellum. These areas were selected for their different dopaminergic activities. After L-dopa loading, DA, DOPAC and HVA were increased in all the structures, but the largest increases were in those tissues with the less dopaminergic activity, while 3-MT increased in the hypothalamus, hippocampus and cerebellum but was lowered in striatum. 3-O-Medopa, which is the direct product of the O-methylation of L-dopa, did not show any specific distribution. The data provide evidence that the striatum, by feed-back mechanisms and specific enzymatic activity, is able to ensure a better regulation of dopaminergic activity than the other structures, thereby overcoming excess L-dopa.